Drilling a well for the production of oil is an involved process, and different types of drill strings may be used to effectuate the drilling. A drill string is a column or string of drill pipe, and the term drill string is loosely applied to the assembled collection of the drill pipe, drill collars, and a drill bit. Drill collars are thick walled pipes that, by virtue of their heavy weight, aid the drill bit in the drilling process. Drilling fluid, which is also known as “mud” by those versed in the art and which consists of carefully tailored solids and chemicals, is pumped down the inside of the hollow drill string. The mud cools the drill bit as it drills, stabilizes the rock in the well walls, and lifts the rock cuttings generated by the drilling up to the surface. The mud can then be recycled and re-used. Instead of a rigid drill pipe, the drill string may comprise flexible coiled tubing. A drill string with a rigid drill pipe generally has to be assembled joint by joint, the successive sections being added with increasing depth of the well; a coiled tubing drilling string, on the other hand, comprises flexible tubing instead of the rigid drill pipe, and need not be assembled joint by joint. A coiled tubing drilling string, therefore, can be tripped in and out of the well at a much faster speed than a drill string with a rigid drill pipe. Similarly, hybrid drill strings, which combine the rigidity of the drill pipe but reduce, if not eliminate, the need to assemble the pipe in parts, may also be employed. Coiled tubing drill strings and hybrid coiled tubing drill strings are known in the art.
Once an oil well is drilled, it may be plugged and abandoned as a dry hole. If, however, oil is to be produced from the well, the well must generally undergo a process referred to as “well completion.” To complete the well, the hole of the well may be cased. Casing involves aligning the wall of the well with hollow pipes made of steel or other suitable materials. Generally, these pipes are of different diameters, which are joined together to make a continuous hollow tube. The diameters of these pipes are dependent upon the depth or level of the well, and are selected under a program referred to as a “casing program.”
FIG. 1 depicts a conventional casing program, and shows how the pipes decrease in diameter with increasing well depth. A conductor pipe 10 has the greatest diameter, and is connected to surface casing 12. The surface casing 12 is in-turn connected to an intermediate casing 14, which is adjoined to a production casing 16. As can be seen, the surface casing 12 has a greater diameter than the intermediate casing 14, and the intermediate casing 14 has a greater diameter than the production casing 16. Casing is integral for the production of oil from a well, as without the casing, the well may collapse and close. Moreover, casing protects the well stream from outside incumbents, such as water or sand, et cetera. The casing is cemented to the walls of the well, which helps to permanently position the casing within the well. Cement slurry, which consists of cement and certain additives, is pumped into the well. The cement slurry displaces the existing mud in the well, and seals the outside of the different casings to the well hole walls.
The well-completion may be of different types. Open-hole completion refers to a well that is drilled to the top of the hydrocarbon reservoir where it is not cased. Open-hole completions are generally used for reservoirs that are well-known and defined. On the other hand, cased-hole completions require the casing to be run into the reservoir. After the cement slurry dries, perforations 18 are created in the sides of the well by a perforation gun. These perforations 18 perforate through the production casing 16 and the cement, and allow the hydrocarbons outside the well hole to enter into the well stream. Tubing 20 may then be used to bring the oil up to the surface. A wellhead and a Christmas tree are generally installed at the surface of the well, and include tubing heads, casing heads, valve controls, et cetera, to provide surface control of the subsurface conditions of the well.
Sometimes, because of a miscalculation, malfunction, unexpected subsurface conditions, et cetera, a blowout occurs. A blowout is the uncontrolled release of crude oil and/or natural gas from an oil well or gas well after pressure control systems have failed. Often, to remedy the situation, a relief well is drilled close to the production well. Drilling a relief well that attempts to penetrate the rather narrow pipe of the blowout well that is buried in sea-bed many thousands of feet below the sea floor is a complex and timely process, which does not have a very high probability of success. The relief well trajectory has to be guided with electromagnetic signals, and the drilling bit for the relief well must be directed until it is running adjacent and parallel to the blowout well in preparation for penetrating the casing of the blowout well. Next, the relief well must inject the blowout well with drilling mud and cement in an attempt to stem the flow of oil and gas under very high pressure. As manifested by recent spills, the development and implementation of plans for such an effort may take many months, and have not always been successful for various reasons, including for example, insufficient density of the drilling mud.